1. Field of the Invention
This invention relates to the manufacture of ceramic honeycomb structures used as particulate traps and heat exchangers, and in particular to forming the honeycomb structures from aqueous ceramic solutions that include ceramic or batch cross-link agents therein that promote cross-linking of the materials used to construct the honeycomb structure, thereby increasing the structural integrity of the same.
2. Description of Related Art
Honeycomb structures having traverse cross-sectional cellular densities of approximately 1/10 to 100 cells or more per square centimeter have several uses, including solid particulate filter bodies and stationary heat exchangers. Such uses require selected cells of the structure to be sealed or plugged by manifolding and the like at one or both of the respective ends thereof.
Reference numeral 10 (FIG. 1) generally designates a solid particular filter body that is generally well known and that may be fabricated utilizing a method as described below. The filter body 10 includes a honeycomb structure 12 formed by a matrix of intersecting, thin, porous walls 14 surrounded by an outer wall 15, which in the illustrated example is provided a circular cross-sectional configuration. The walls 14 extend across and between a first end 13 that includes a first end face 18, and a second end 17 that includes an opposing second end face 20, and form a large number of adjoining hollow passages or cell channels 22 which also extend between and are open at the end faces 18, 20 of the filter body 10. To form the filter 10 (FIGS. 2 and 3), one end of each of the cells 22 is sealed, a first subset 24 of the cells 22 being sealed at the first end face 18, and a second subset 26 of the cells 22 being sealed at the second end face 20. Either of the end faces 18, 20 may be used as the inlet face of resulting filter 10.
A typical method for manufacturing the honeycomb structure 12 described above includes the steps of batch mixing 28 (FIG. 4) an aqueous ceramic solution used to form the walls 14, 15 of the honeycomb structures 12, extruding 30 the aqueous ceramic solution through die sets thereby forming a green ware honeycomb structure, and cutting 32 the green ware honeycomb structure into a particular length. The method also includes firing 34 of the green ware honeycomb structure to form a hardened honeycomb structure, cutting 36 the hardened honeycomb structure 12 to provide finished end faces, removing the dust 38 created during the cutting process 36, masking 40 the end faces 18, 20 of the honeycomb structure 12, plugging 42 certain cell channels 22 of the honeycomb structure 12, firing 46 of the plugged honeycomb structure 12 to form a hardened filter 10 and machining 48 an outer skin of the filter 10. The method further includes testing 50 the filter 10 and packaging 52 the same for shipment. As is evident from the above, the current method used to manufacture the filter 10 is time intensive, lengthy and costly, and that any steps or procedures available to reduce the overall cycle time associated with manufacturing these filters while maintaining manufacturing and filter quality standards, would be extremely advantageous.
In operation, contaminated fluid is brought under pressure to an inlet face (either of the end faces 18, 20) and enters the filter 10 via those cell channels 22 which have an open end at the given inlet face. Because these cell channels 22 are sealed at the opposite end face, i.e., the outlet face of the body, the contaminated fluid is forced through thin porous walls 14 into adjoining cell channels 22 which are sealed at the inlet face and open at the outlet face. The solid particulate contaminate in the fluid, which is too large to pass through the porous openings in the walls 14, is left behind and a cleansed fluid exits the filter 10 through the outlet cell channels 24 and is ready for use.
For the mass production of such filters and heat exchangers, it is highly desirable to be able to seal selected cell channel ends as rapidly and as inexpensively as possible, while maintaining certain quality standards in the resultant filters. As noted above, heretofore the mass production of these filters included forming of a green ware honeycomb structure followed by a first firing process in order to provide a hardened honeycomb structure, and then the plugging of the hardened honeycomb structure followed by a second firing process. As the firing or curing processes are ultimately the most expensive portion of the overall manufacturing process, it is desirable to reduce the amount of time involved therewith.
Another previous approach to plugging the honeycomb structure 12 to form the filter 10 has included the cold-set plugging of the material used to seal the ends 18, 20 of the honeycomb structure 12. However, this particular approach includes significant risks as the cold-set plugs do not experience the thermal history of the honeycomb structure 12 during the manufacturing process, and may therefore prove less durable during operations in the field.
A final approach includes the plugging of the honeycomb structure 12 prior to the firing or drying thereof to form a plugged green ware honeycomb structure. Heretofore, significant drawbacks to this approach have included the smearing of the honeycomb structure 12 near the end faces 18, 20, and a weak interface between the plug material and the walls 14 forming the web within the honeycomb structure 12. Specifically, the typical composition used for forming the honeycomb structure 12 is not water resistant, thereby allowing the associated walls 14 to absorb water from the plugging material and be distorted during the plugging process. For those materials which are non-water based, typical results have been a poor interface between the plug material and the walls 14, thereby resulting in an overall weak filter that does not perform well in field conditions.
A method for manufacturing a honeycomb structure that may be utilized as a filter, such as those used as particulate traps for diesel engines, is desired that reduces the overall manufacturing time by reducing the amount of time associated with firing or curing of the honeycomb structure while simultaneously maintaining or improving the structural integrity of the resultant filter.